Since the low-carbon economy has become a global theme, energy-saving materials are increasingly favored by people. In the field of energy consumption, building energy consumption accounts for nearly 40% of total energy consumption, and the energy loss through the glass doors and windows in the building energy consumption reaches more than 50%. It means that glass windows and doors become the largest energy vulnerability of buildings. The primary energy consumption in the building energy consumption is spent in heating and cooling. Thus, improving windows thermal insulation performance is an effective way to reduce building energy consumption.
The radiation wavelength range of sunlight reaching the ground is about 200-2500 nm, in which 200-400 nm is ultraviolet ray, 400-800 nm is visible light, and 800-2500 nm is near-infrared ray. The near-infrared can be divided into short-wave near-infrared (800-1100 nm) and long-wave near-infrared (1100-2500 nm). Moreover, the energy distribution of solar radiation in the visible region, near-infrared region, and the ultraviolet region is about 45%, 50% and 5%, respectively. The use of energy-saving windows and doors is to block ultraviolet light, near-infrared light, and thereby block the heat radiation without affecting lighting.
In order to meet energy requirements, insulating glass has been used in cars, ships and buildings. Conventional insulating glass production methods are mainly float-line magnetron sputtering method and chemical vapor deposition (CVD) method. The disadvantages of these two methods are high cost which is difficult to scale up, and the vastly used metals are easily oxidized, leading to the short life of the product. Coating the ordinary glass with transparent insulation coating or pasting transparent insulation film on the ordinary glass can achieve the same insulation performance with low production cost and easy construction, which is an ideal alternative to traditional insulating glass. The function of transparent insulation coating or film is to allow visible light to pass while shielding the ultraviolet and infrared.
VIB Group metals include chromium (Cr), molybdenum (Mo), and tungsten (W). In 1949, A. Magne Li (Arkiv. Kemi, 1949, 1:213) synthesized tungstate KxWO3 (0<x<1) with octahedra as the basic structural unit, and the tungstate and the compounds with similar structure were named as tungsten bronze materials due to they has a bronze-like color and bright. It is found that reducing the oxygen content of tungsten oxide (WO3) can realize the absorption of the near-infrared. When tungsten oxide exposed to a reducing atmosphere and an elevated temperature, the structural phase tungsten Magneli suboxide (WO3-x) forms, and under reducing conditions the positive ion is added to the polyhydric WO3, the near-infrared absorption can be achieved. The resulting products are usually a tungsten bronze structure, for example, sodium tungsten bronzes, potassium tungsten bronzes, cesium tungsten bronze.
MoO3 in coloration state is called molybdenum bronze, which open circuit memory is better than tungsten bronze structure, but its oxidation process is slow. Also the absorption spectrum of MoO3 have a more smooth curve in the visible region, the absorption peak is at 550 nm, which is closer to the light band that human eye is sensitive to, which makes it easier for human eyes to adapt to color change, therefore, it has a gentle neutral hue. Currently, it is generally believed that in its electrochromic process, Mo is in states of Mo6+ and Mo5+ with the following formula:MoO3+xMe++xe−=MeMo6+(1−x)Mo5+xO3
Wherein, Me+=H+, Li+, Na+, etc. When Me+ and e− are injected simultaneously, the color of MoO3 changes from colorless into dark blue.
U.S. Patent US20110248225 discloses potassium cesium tungsten bronze particles of the formula KxCsyWOz (x+y≤1, 2≤z≤3) and a process for preparing potassium cesium tungsten bronze particles in a plasma torch.
Chinese Patent Application CN102145980A discloses an alkali metal and halogen co-doped tungsten oxide materials with the formula of MxWO3-yAy (M: an alkali metal, W: tungsten, O: oxygen, A: a halogen element, 0<x≤1, 0<y≤0.5) and a method for preparing the same under hydrogen-reducing conditions.
Chinese Patent Application CN102320662A discloses a method for preparing cesium tungsten bronze powder, comprising the following steps: a precursor solution comprising tungstate, cesium carbonate and reducing substances (preferably citric acid) is prepared, where the Cs/W molar ratio is 0.01-0.35:1, the solvent is water or a mixture of ethanol and water with a volume ratio 1:4 to 4:1 thereof; the precursor solution is then placed in an autoclave at 180-200° C. for 1-3 d, the resulting precipitate is post-treatment to obtain cesium tungsten bronze powder with particle size of 100-1300 nm.
However, there remains a need to provide stably dispersed VIB Group metal oxide doped nanoparticles and dispersions which have high transparency and also can block shortwave and long-wave near-infrared, and can be used for glass coating or film. And a need of the methods which is economically feasible and can be scaled up easily to prepare VIB Group metal oxide doped nanoparticles and their dispersions.